WiMAX 802.16 tutorial
- an overview, summary or tutorial about WiMAX, the broadband wireless
access (bwa) technology using IEEE 802.16 - 802.16d and 802.16e
WiMAX is a broadband wireless data communications technology
based around the IEE 802.16 standard providing high speed data over a wide area.
The letters of WiMAX stand for Worldwide Interoperability for Microwave Access
(AXess), and it is a technology for point to multipoint wireless networking.
WiMAX technology is expected to meet the needs of a large variety of users from
those in developed nations wanting to install a new high speed data network very
cheaply without the cost and time required to install a wired network, to those
in rural areas needing fast access where wired solutions may not be viable
because of the distances and costs involved. Additionally it is being used for
mobile applications, proving high speed data to users on the move.
The standard for WiMAX is a standard for Wireless Area
Metropolitan Networks (WMANs) that has been developed by working group number 16
of IEEE 802, specializing in point-to-multipoint broadband wireless access.
Initially 802.16a was developed and launched, but now it has been further
refined. 802.16d or 802.16-2004 was released as a refined version of the 802.16a
standard aimed at fixed applications. Another version of the standard, 802.16e
or 802.16-2005 was also released and aimed at the roaming and mobile markets.
Although based around the IEEE standard 802.16, WiMAX
technology also addresses the European Telecommunications Standards Institute
(ETSI) HiperMAN (HIgh PErformance Radio Metropolitan Area Network) standard.
This will make the standard a truly international standard and one which has the
backing of the industry leaders in these fields
WiMAX Forum
The WiMAX Forum is a wireless industry consortium with a
growing number of members including many industry leaders. It has been set up to
support and develop WiMAX technology worldwide, bring common standards across
the globe to enable WiMAX to become an established worldwide technology.
One of the aims of the forum is to enable a standard to be
adopted that will enable full interoperability between products. Learning from
the problems of poor interoperability experienced with previous wireless
standards, and the impact that this had on take up, the WiMAX Forum aims to
prevent this from happening. Ultimately vendors will be able to have products
certified under the auspices of the Forum, and then be able to advertise their
products as "Forum Certified".
Although WiMAX technology will support traffic based on
transport technologies ranging from Ethernet, Internet Protocol (IP), and
Asynchronous Transfer Mode (ATM), the Forum will only certify the IP-related
elements of the 802.16 products. The focus is on IP operations because this is
the now the main protocol that is used.
WiMAX flavours
Since its initial conception, new applications for WiMAX have
been developed and as a result there are two "flavours" of WiMAX that are
available:
- 802.16d (802.16-2004)
- 802.16e (802.16-2005)
The two flavours of WiMAX are used for different applications
and although they are based on the same standard, the implementation of each has
been optimised to suit its particular application.
- 802.16d - DSL replacement The 802.16d version of WiMAX
is often referred to as 802.16-2004 and it is closer to what may be termed
the original version of WiMAX defined under 802.16a. It is aimed at fixed
applications and providing a wireless equivalent of DSL broadband data. In
fact the WiMAX Forum describes the technology as "a standards-based
technology enabling the delivery of last mile wireless broadband access as
an alternative to cable and DSL."
802.16d is able to provide data rates of up to 75 Mbps and as a result it is
ideal for fixed, DSL replacement applications. It may also be used for
backhaul where the final data may be distributed further to individual
users. Cell radii are typically up to 75 km.
- 802.16e - Nomadic / Mobile While 802.16 / WiMAX was
originally envisaged as being a fixed only technology, with the need for
people on the move requiring high speed data at a cost less than that
provided by cellular services and opportunity for a mobile version of WiMAX
was seen and 802.16e was developed. This standard is also widely known as
802.16-2005. It currently provides the ability for users to connect to a
WiMAX cell from a variety of locations, and there are future enhancements to
provide cell handover.
802.16e is able to provide data rates up to 15 Mbps and the cell radius
distances are typically between 2 and 4 km.
Air Interface
WiMAX uses OFDM (Orthogonal Frequency Division Multiplex) as
its modulation scheme. For 802.16d, 256 carriers are used, but for 802.16e the
system is scaleable according to the conditions and requirements.
More advanced versions including 802.16e utilise MIMO
(Multiple Input Multiple Output) and as a result support for multiple antenna.
The use of these techniques provides potential benefits in terms of coverage,
self installation, power consumption, frequency re-use and bandwidth efficiency.
Note on OFDM:
Orthogonal Frequency Division Multiplex (OFDM) is a
form of transmission that uses a large number of close spaced carriers
that are modulated with low rate data. Normally these signals would be
expected to interfere with each other, but by making the signals
orthogonal to each another there is no mutual interference. This is
achieved by having the carrier spacing equal to the reciprocal of the
symbol period. This means that when the signals are demodulated they
will have a whole number of cycles in the symbol period and their
contribution will sum to zero - in other words there is no interference
contribution. The data to be transmitted is split across all the
carriers and this means that by using error correction techniques, if
some of the carriers are lost due to multi-path effects, then the data
can be reconstructed. Additionally having data carried at a low rate
across all the carriers means that the effects of reflections and
inter-symbol interference can be overcome. It also means that single
frequency networks, where all transmitters can transmit on the same
channel can be implemented.
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Frequencies used
The IEEE 802.16 WiMAX standard allows data transmission using
multiple broadband frequency ranges. The original 802.16a standard specified
transmissions in the range 10 - 66 GHz, but 802.16d allowed lower frequencies in
the range 2 to 11 GHz. The lower frequencies used in the later specifications
means that the signals suffer less from attenuation and therefore they provide
improved range and better coverage within buildings. This brings many benefits
to those using these data links within buildings and means that external
antennas are not required.
Different bands are available for WiMAX applications in
different parts of the world. The frequencies commonly used are 3.5 and 5.8 GHz
for 802.16d and 2.3, 2.5 and 3.5 GHz for 802.16e but the use depends upon the
countries:
| Region |
Frequency
Bands (GHz) |
Comments |
| Canada |
2.3
2.5
3.5
5.8 |
|
| USA |
2.3
2.5
5.8 |
|
| Central and South America |
2.5
3.5
5.8 |
The spectrum is very fragmented and
allocations vary from country to country |
| Europe |
2.5
3.5
5.8 |
The spectrum is very fragmented and
varies from country to country. The 2.5 GHz allocation is currently
allocated to IMT 2000. 5.8 GHz is also not available in most European
countries. |
| Middle East and Africa |
2.5
5.8 |
The spectrum is very fragmented. |
| Russia |
2.5
3.5
5.8 |
The 2.5 GHz allocation is currently
allocated to IMT 2000. |
Asia Pacific
(inc China, India, Australia, etc) |
2.3
2.5
3.3
3.5
5.8 |
The spectrum is very fragmented and
varies between countries. |
Current major spectrum allocations for WiMAX worldwide
Competition for WiMAX
The competition with WiMAX, 802.16 depends upon the type or
flavour of WiMAX being used. Although initially it was thought that there could
be significant competition with Wi-Fi, there are other areas to which WiMAX is
posing a threat.
- DSL cable lines WiMAX is able to provide high speed data
links to users and in this way it can pose a threat to DSL cable operators.
- Cell phone operators Cell phone operators see the new mobile
version of WiMAX as a significant threat. It is offering data download
speeds in excess of those that can be offered even using the latest cellular
UMTS HSPA (High Speed Packet Access) systems that are being deployed. WiMAX
is also able to offer greater cost efficiency. As a result, cellular
operators are looking at ways of defending themselves against the possible
use of WiMAX.
WiMAX Overview
WiMAX is now being deployed in many areas and while it was
initially seen as yet another wireless standard that might fall into the
background, it is now emerging as a major front runner and posing threats to
other areas of the industry. It is being seen by many as a real competitor to
3G, being able to offer data transfer speeds that are more in keeping with LTE
(Long Term Evolution) the new 4G standard that is starting to be developed. In
view of this, very much more will be seen of WiMAX 802.16 in both its 802.16d
and 802.16e variants in the coming years.
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